Wiper mechanism for coating machines and process



March 14, 1933. p. B, BRADNER 1,901,

WIPE-R MECHANISM FOR COATING MACHINES AND PROCESS Filed Feb. 1932gwomto;

- at removing the excess Patented Mar. '14, 33 c UNITED srAras PATIENToi-r ce nommn 3.3mm, or oxroan, 0310, rissm'non. 'ro THE cnmrrorrcoa'rnn rum 7 comm, or mun-r011, 01110, a coarona'rrorr or one WEBMECHANISM. FOR GCTATING AND PROCESS Application filed February a, 1932.Serial no. 591,207..

r This invention relates to an improvement in coating machines adaptedfor use 111 ap- Y plying to a moving surface a coating or layer positionis applied to a web of paper and all except the desired quantity isremoved from the aper by means of a doctor member whose sur ace moves inthe op osite direction to the go paper. Instead of app ying the coatingdi-* rectly tothe paper, the desired film of coat- 1 ing may be formedon an applicator member by applying an excess of the aqueous coatingcomposition to said applicator member and y means of a doctor membermoving in the opposite direction to the applicator member, andthereafter transferring the film of coating from the applicator memberto a web of paper moving in 80 the opposite direction thereto. Thelatter process is disclosed in my copending application, No. 581,955,filed December 18, 1931.

I11 either case, forthe proper functioning of the doctor member, it isessential that 5 there be provided means associated therewith for wipingor cleaning the surface of the same whereby the doctormember maycontinuously present a relatively clean surface to the coatingcomposition on which it acts. There 4 has been provided for this purposea wiper blade maintained in contactwith the useful surface of the doctormember.

The heretofore suggested wiping or cleaning means has not proven to bewhollysatisfactory in commercial operation: it (the aforesaid singlewiper blade; is dificult to control, requires careful a justment, andmust be replaced rather frequently; Whenever the wiper blade failstoremove all of the coating adhering to the doctor member surface, theamounts not removed form streaks or spots in the resulting coating: sucha result in the case of a fine coating operation requlring a highquality product makes necessary the rejection of relatively largeamounts of the coated. product.- This is especially true in theproduction of high quality coated papers where any minute irregu larityin the coating makes the product un salable.

I I have found that the above and other disadvantages resulting from anattempt to cleanthe doctor member surface by, means of'only a singlewiper blade may be very largely overcome and that improved coated papermay be produced by providing the doctor member with a second wipermechanism in series with the first and by treating, or at leastthoroughly wetting, the doctor surface w th a washing liquid between thetwo wipers. The said washing liquid ma be water or some aqueoussolution. I ave found that adoctor member .wetted with liquid is muchmore easily cleaned than is one covered with a film of coating.

. 7 Furthermore, I have discovered that the second wiping in mostinstances need not re- 1 move the last traces of the washing liquid,

but rather that the coatings may be improved in smoothness or flatnessof lay by leaving over the whole surface of the doctor member.

a film. of the washing liquid. It may be ob-i served, in thisconnection,that if the doctor 'member surface carries a film of liquidin some portions but is wholly dry in other portions there usuallyresults a corresponding unevenness of smoothing of the coating with theconsequent production of a s otted, streaked, orotherwise blemishedcoate product. Accordingly, rather than to attempt to 9 layer: oneportion or area of the doctor mem ber surface may carry a somewhatgreater quantity of the wetting liquid than another without detriment tothe smoothness ofthe coating (provided, of course, that no rela-' tivelygreat quantity of the wetting liquid be carried past the second wipingmeans). This is especially advantageous, because it is a very difficulttask continuously to wipe the doctor member surface wholly dry at allpoints thereon. Therefore, I prefer to take advantage of the phenomenonabove noted by simply at adjusting the second wiping means .50 t

a thin film of the washing liquid passes the same at all times.

An embodiment of the invention is illustrated in the accompanyingdrawing, in which:

The figure is a diagrammatic representation of an apparatus for carryingout the process.

In the drawing 1 is a web of paper which passes around an applicatorroll 2 in the direction of the arrow. 3 is a substantially rigidlysurfaced doctor roll which'is adjacent to roll 2 and is revolvable inthe same angular direction as the applicator roll 2; that is to say, thesurfaces of the two rolls are traveling in opposite directions at theirpoints of closest approach, i. e., the nip. Between rolls 2 and 3 is apool of aqueous mineral coating composition 4 which is supplied by adelivery pipe 5.

6 and 7 are wiper blades, which may be of rubber or have a rubber edge.These wiper blades 6 and 7 are spaced apart fromeach' other and areadjustably held in association with doctor roll-3 by any suitable meanssuch as the adjustable supports 6a and 7 (1, respectively. At anysuitable point between blades 6 and 7 is a pipe 8 connected to a sourceof water under pressure and having perforations through that portion ofits wall which is adjacent roll 3. The pipe 8 is substantially parallelwith the axis of roll 3.

In operation, the web of paper 1 to be coated is passed around roll 2and through the nip between rolls 2 and 3, said rolls 2 and 3 beingrevolved in the same angular direc-' tion and at any desired speeds. Apool of a ueous mineral coating composition 4 is est'a lished betweenrolls 2 and 3, and maintained by delivery theretoof amounts of thecomposition from a source thereof by delivery vpipe 5: the web of paper1 thus passing through said pool. Coating composition which may becarried out of said pool by roll 3 is wi ed off of said roll by wiperblade 6- sprayed thereon from pipe 8, and any solids and excess ofliquid thereon are removed by.

the second wiper blade 7, whichis so adjustable as to pass only a verythin film of water, thus presenting a coating-free but waterfilmedsurface for smoothing the layer of coating carried into the nip betweenrolls 2 and 3 by the web 1. So long as the surface of doctor roll 3 isnot dry in some areas and wetted in others, the resultin coating is notstreaked or spotted. It is, 0 course, within the scope of the inventionto so adjust the second wiper that there will be no film of water on thedoctor surface after passing the second wiper, but this is not asconvenient a method of operation. 7

Instead of passing the paper through the nip of the rolls 2 and 3, thedesired film of coating may be formed directly on the applicator roll 2and thereafter transferred to the paper by a wiping action. Also eitherthe applicator member or the doctor member may be in the form of a belt.In any of these modifications of method and apparatus, the doc tormember is given a double wiping treatment with a washing operation interosed between the wipers. Also in place 0 a wiper blade other wipingmeans may be employed, such as for example, a resilient surfaced roll,and the washing liquid may be delivered to and distributed on thesurface of the doctor member by other means than the perforated pipeshown. I

In this connection, I have observed that a somewhat higher doctorsurface speed is required to avoid ridges in the coated pa er when thedoctor roll surface carries a m of water than when it is dry. On theother hand, if the doctor roll surface is wetted with a film of liquidhaving a lower surface tension than that of the aqueous mineral coatingcomposition employed, a lower doctor roll speed is required to avoidrippled coatings.

'I claim:

1. In a process of coating involving the operations of applying .anexcess of coating composition to a moving surface, removing all exceptthe desired weight of coating therefrom by means of a doctor membermoving in the opposite direction to said moving surface at the point ofclosest approach thereto, the method of cleaning the doctor membersurface and preparing it for reuse, which consists essentially. inwiping it, then thor oughly wetting it'with a washing liquid and againwiping it.

2. In a process of'coating involving the operations of applying-anexcessof coating composition to a moving surface, removing all except thedesired weight ofcoating therefrom by means of a doctor member moving inthe opposite direction to said movingsurface at the point of closestapproach thereto, the method of cleaning the doctor member surface andpreparing it for reuse, which consists essentially in wiping it, thenthoroughly wetting it with a washing liquid, and finally wiping anysolids and excess of washing liquid from it whereby to present for reusea surface free of solids and carrying there- 7 on a film of the washingliquid.

3. In a process of coating involving the operations of applying anexcessof coating composition to a moving surface, removing all except'thedesired weight of coating therefrom by means of a doctor member movinginthe opposite direction to said move ng surface at the point of closestapproach 4 thereto, the method of cleaning the doctor member surface andpreparing it for reuse, which consists essentially in wiping it, thenthoroughly wetting it with water, and finally wiping any solids andexcess of water from it whereby to present for reuse a surface free ofsolids and carrying thereon a film of water.

4. In a process of coating involving the operations of applying anexcess of coating composition to a moving surface, removing all exceptthe desired weight of coating therefrom by means of a doctor membermoving in the opposite direction to said moving surfaceat the point ofclosest approach thereto, the method of cleaning the doctor membersurface and preparing it for reuse, which consists essentially in wipingit, then-wash ing it with a stream of water, and finally wiping anysolids and excess of water from it wherebyto present for reuse a surfacefree of solids and carrying thereon a film of water.

5. In an apparatus for formingonamoving v surface an even layer ofcoating composition said doctor roll of plural means for cleanwith thesurface of containing a liquid vehicle, including a movable doctormember, the association with said doctor member of plural means forcleaning the surface of the latter and preparing it for reuse which inthe order of their occurrence are a wiping means, a means for deliveringa stream of washing liquid, and a'second wipmg means. a

6. In an apparatus for forming on a moving surface an even layer ofcoating composi tion containing a liquid vehicle, including a rotatabledoctor roll, the association with a said doctor roll of plural means forcleaning the surface of the latter and preparing it for reuse which inthe order of their occurrence are a wiping means, a means for deliveringa stream of washing liquid, anda second wiping means.

7 In an apparatus for forming on a moving surface an even layer ofcoating composition containing a liquid vehicle, including, a rotatable,doctor roll, the association with

